Genital infection by the obligate intracellular pathogen, Chlamydia trachomatis, is the most common bacterial sexually transmitted disease (STD) in the United States, with four million reported annual cases that cost over $2 billion. Of major pathophysiological significance is the propensity for cervical infection in women to spread into the upper genital tract, provoking serious complications such as pelvic inflammatory disease, fallopian tube scarring, ectopic pregnancy and infertility. Also, the frequently asymptomatic infections do cause severe irreversible complications to be the first evidence of an infection. There are concerns that genital chlamydial disease, like certain other STDs, such as AIDS and gonococcal disease, may pose a serious threat to human reproduction, well-being and healthcare costs. Current control and prevention strategies target frequent screening for early detection and treatment, and development of vaccines as the priority. The search for a chlamydial vaccine has led to extensive research to define the crucial immune effectors in anti-chlamydial immunity, identify antigens that elicit protective immunity, and design effective methods of vaccine delivery. Our research has been focused on identifying the relevant immune parameters in chlamydial immunity and elucidating the mechanism(s) of intraepithelial inhibition of chlamydiae. Our findings and reports by others have culminated in a new paradigm for designing vaccines against Chlamydia based on the induction of local mucosal TH1 response. The major challenge at this stage is to select an appropriate immunogen(s) and design an effective delivery system, to induce high levels of local genital mucosal Th1 response to maintain long-term immunity. Accordingly, this proposal uses immunological, genetic engineering, molecular, cellular and biochemical techniques to investigate the central hypothesis that protective anti-chlamydial immunity will be established if immunogenic chlamydial antigen(s) are effectively delivered to induce high frequency of specific Th1 cells in the genital mucosa. Specific studies planned will use genetically engineered and wild type mice to: (a) investigate the efficacy of genetically designed recombinant multi-subunit vaccines composed of mucosal bacterial ghosts co-expressing multiple membrane proteins of C. trachomatis; (b) assess the therapeutic benefits of an immunotherapeutic cellular vaccine based on IL-lO gene-suppressed dendritic cells presenting antigens for inducing high frequency of specific Th1 response, as an alternative therapeutic vaccine for C. trachomatis; (c) identify the major mucosal inductive sites, antigen-presenting cells and other accessory cells crucial for Th1 activation; and (d) define the molecular and cellular elements regulating Th1 activation, trafficking and recruitment into the genital mucosa following effective cellular and subunit vaccination against C. trachomatis. Results from these studies will likely lead to the development of a reliable vaccine regimen against Chlamydia, which should have major implications for the genital, ocular, and lung infections and their complications.